In general, an OLED comprises an anode, a cathode and an emission layer interposed between the anode and the cathode. When a voltage is applied between the anode and the cathode, holes and electrons are injected into the emission layer, and then combined to create exitons which decay radiatively. This radiation is called electroluminescence (EL)
The OLED may be classified as a passive matrix (hereinafter, referred to as PM) type and an active matrix (hereinafter, referred to as AM) type, based on a manner for driving pixels of N×M arranged in a matrix. The AM type OLED, also referred to as an AMOLED, may have less power consumption and higher resolution then the PM type, and it may be suitable for large area implementation.
FIG. 1 shows a cross-sectional view illustrating a structure and a method for fabricating a conventional AMOLED.
Referring to FIG. 1, a buffer layer 105 is formed on an insulation substrate 100 having an emitting region A and a non-emitting region B. An active layer 171 has a source region 171a, a drain region 170b, and a channel region 171c and is formed on the buffer layer 105 of the non-emitting region B. A gate-insulating layer 173 is formed on the active layer 171, and a gate electrode 175 is formed on the gate-insulating layer 173 to correspond to the channel region 171c. A first insulation layer 176 is formed over the entire surface of the substrate, including the gate electrode 175. Contact holes exposing each of the source and drain regions 171a and 171b are formed in the first insulation layer 176. A source electrode 177 and a drain electrode 178 are formed on the first insulation layer 176 to connect to the source and the drain regions 171a and 171b through the contact holes, respectively. The active layer 171, the gate electrode 175, the source electrode 177 and the drain electrode 178 constitute a driving TFT 170.
A second insulation layer 180 is then formed over the entire surface of the substrate, including the source and drain electrodes 177 and 178, and a via hole 183 is formed in the second insulation layer 180 to expose the drain electrode 178. A pixel electrode 191 is then formed on the second insulation layer 180 of the emitting region A, which is connected to the exposed drain electrode 178 through the via hole 183. The pixel electrode 191 has a bent portion 191a within the via hole 183. A pixel defining layer 185 is formed to cover the bent portion 191a. An opening P for exposing the pixel electrode 191 at a position spaced from the via hole 183, namely the bent portion 191a, is formed in the pixel defining layer 185. An organic emission layer 195 is then formed over the exposed pixel electrode 191 within the opening P, and an opposite electrode 199 is formed on the organic emission layer 195. As a result, an organic electroluminescent diode 190 having the pixel electrode 191, the organic emission layer 195, and the opposite electrode 199 is formed. The organic electroluminescent diode 190 is connected to and driven by the driving TFT 170 through the via hole 183.
Since the pixel defining layer 185 is formed to cover the bent portion 191a of the pixel electrode 191, the organic emission layer 195 is not formed on the bent portion 191a and prevents the organic emission layer 195 from being bent along the bent portion 191a of the pixel electrode 191. Therefore, degradation of the organic emission layer 195 due to the bend may be reduced or prohibited. However, the pixel defining layer 185 should be formed when the driving TFT 170 and the organic electroluminescent diode 190 are connected through the via hole 183, which increases the number of processes and masks required for the processes and increases the production cost.
In addition, the bent portion 191a of the pixel electrode 191 may cause defects due to a concentrated electric field at the bent portion 191a when driving the OLED.